1. Field of the Invention (Technical Field)
The present invention relates to control of the heart, in particular defibrillation, pacing, and cardiac paralysis.
2. Background Art
Existing devices for treating cardiac arrhythmia require deployment of high voltages which can, and often do, cause injury to the patient. The present invention permits utilization of low voltages and greatly decrease the risk of further injury to the patient.
An arrhythmia is any abnormal electrical contraction of heart. Particular arrhythmias include: asystolexe2x80x94no beat at all or xe2x80x9cflat-linexe2x80x9d on monitor; bradycardiaxe2x80x94slow beat, less than 60 beats per minute; tachycardiaxe2x80x94fast beat, over 100 beats per minute; and fibrillationxe2x80x94life threatening chaotic heart action in which the heart twitches or quivers rapidly and is unable to pump efficiently.
During fibrillation, less blood is circulating and thus all systems of the human or animal body are at risk. The longer fibrillation continues unchecked the more likely death will occur. For every minute of fibrillation, a 10% reduction of life potential is subtracted, i.e., ten minutes results almost certain death. During fibrillation the electrical system of the heart is disorganized and erratic. The normal rhythmic beat is totally lost. Serious life threatening events begin to occur. Breathing becomes erratic and then stops as electrical failure begins. Shortly the inadequate circulation of blood causes organs and tissues to be oxygen starved and cell death begins. When brain and heart muscle oxygen starvation reach crisis points they begin to die and hence the entire body begins to die. At some point the heart fibrillations are not reversible and death of the human or animal occurs. It is important to stop fibrillation and to restart or regain the same level of heart contractions to oxygenate the entire body properly.
Fibrillation is currently typically treated by an electronic defibrillator which delivers a shock via two hand-held paddles. This process is familiar to those who view medical television shows and witness a shock so great that the entire body jumps. This shock is about 2,000 to 5,600 volts for external shocks and 310 to 750 volts for internal defibrillators. Repeated use of such large electrical shocks likely may damage the nervous system to such an extent that disabilities shall be present even if the patient lives. The popular conception is that a defibrillator xe2x80x9cputsxe2x80x9d a heart beat into a stopped heart. Actually, a defibrillator stops the quivering heart, after which, but not always, the heart may resume a slow beat (bradycardia). Paramedics then can use medications to speed up the heart and/or administer an emergency external pacemaker while transporting the victim to a hospital.
In the science of electromyography there is a graphical presentation of fibrillation on a visual monitor of a heart muscle being affected by a monophasic, biphasic or triphasic spike usually of 25 to 100 microvolts in amplitude and each less than 2 milliseconds in duration. These represent uncoordinated contractions of heart muscle (myocardium) fibers. This is a degrading and dangerous state and does require electrical intervention plus oxygen and cardiac medications in an effort to stabilize or regain a normal heart beat. Perhaps 40% of heart attack victims are in fibrillation when a paramedic arrives. Another 40% might be in bradycardia, tachycardia or asystolic status. The other 20% might have plugged heart blood vessels, bleeding, or other conditions that are not related to the electrical function of the heart muscle.
The present invention provides devices and methods whereby substantially lower voltages and currents may be used to successfully treat heart muscle arrhythmias.
All individual organs of the body are electrochemical in nature and operate on something approximating one volt to conduct their respective duties. Certainly the action of the myocardium (muscular contractile body of the heart) which contracts about one billion times in a life span, also conducts its business of pumping blood utilizing only about one volt of electricity at any point in time. Each beat is a cascading flow of myocardial contractile motions that squeeze blood from the four chambers of the heart and then accept a refilling of blood for the next cycle.
The heart is a pump with a closed system of arteries and veins with a natural duty to circulate oxygenated blood over the entire network of blood vessels. Oxygenated blood is red when it is rich with oxygen loaded into its red cells, called erythrocytes. Blood turns blue as carbon dioxide (CO2) and other waste products are loaded into its red cells, not now called xe2x80x9cblue cellsxe2x80x9d. The returning blue blood is pumped to the lungs to release the CO2 and other gaseous waste products. The red cells immediately uptake oxygen and continue their journey via the heart and into the blood vessels, to cyclicly do it all over again.
State of the art application of electricity for medical therapy to stop the fibrillation or quivering that is often encountered when a paramedic arrives on the scene of a heart attack victim, uses from 1,800 to 5,600 volts with 27 to 75 amps of current. The actual voltage and amperage that reaches the heart varies under Ohm""s law by the resistance of the human or animal body and the integrity of electrode contacts to the body. Ohm""s law states that voltage (V) equals the product of current (I) and resistance (R), or V=IR. Hydration of the skin under the electrodes also plays into the efficiency of the electrical therapy. There is approximately 50 to 150 ohms of resistance in the body depending on the hydration of live tissues. However, the most outer thin layer of dry skin can be 1000 ohms or higher. But high voltage can bust through that skin layer. Obviously the tissue is not as good a conductor as a metallic wire. However, because of the ionic nature of human or animal bodies it is possible to generate a specific waveform and cause it to enter the biological tissue and have an effect. Designers of external defibrillators anticipate a 50-ohm resistance load, but they know it could be somewhat higher.
Despite public perception, most of the people collapsing with heart failure, are not reached in time by paramedics to save them. Those that live because they received early defibrillation are often impaired from the cardiopulmonary resuscitation (CPR) process or by the high-voltage energy applied to their chest. The use of voltages that re in the range of 1,800 to 5,600 volts applied to the closed-bare chest of a human is a risky event. It is also risky to the medical personnel who must stop all contact with the patient or potentially be an electrocution victim themselves. The patient must sustain the large shock which conducts all over the body, with risk of burning out peripheral nerves and injuring any organ or system. There is a question of why such large voltage electric shock therapeutically even makes a positive outcome in the small minority of heart attack victims it saves.
The human body runs on small voltage within all of its systems including the brain and the heart yet all electric shock therapy consists of explosive bursts that are a risk to patient and treatment personnel. xe2x80x9cStand-Clearxe2x80x9d is used by medical personnel to mean keep away or risk dangerous electrocution.
The usual action of the heart electrically begins by the sinoatrial node (SA node) firing a signal that then travels through known conductive pathways while activating contraction events as it goes. The SA node is actually a strip of electrochemical cells located on the radius between the vena cava and the right atrial chamber. Explained in simplicity, the conducted bioelectrical pulse activates in turn the atrioventricular node (AV node) and then respectively to various branches of the cardiac conductive pathways to complete a cardiac cycle from the top atrial chambers of the heart onward to the powerful ventricular chambers. The SA note repeats itself for the next round of activation of the electrical circuits which activate the pumping action of the heart all over again. The heart""s duty is to circulate blood via the contractile ability of its various chambers, of which there are four, to repetitively contract and relax. Contraction pumps blood and relaxation allows the four chambers of the heart to refill with blood. The SA node electrical action is the beginning of the entire electrical activation system which causes the contractile cells which populate the myocardial muscle structure to react to this stimulation in an uncoordinated unison. The action of the contraction occurs more or less in harmony but this does not mean every cell contracts at the same time.
When observing the heart in an open chested subject, be it animal or human, this contraction appears as wave-like motions caused by the unsynchronized actions of myocardial muscle strands shrinking and stretching. The lack of synchrony is only mildly apparent. As the heart contracts cellular events are occurring so fast that the activation of the pumping action occurs with enough cells arriving at maximum shrinkage, contraction, within millionths of a second of each other. The fact that some of the contractile cells are a little late only adds to the final xe2x80x9cpushxe2x80x9d of the blood out of the respective chamber.
The heart is alive so it can be expected that it will not have positive pumping actions that in any way approximate a man-made mechanical pump. The heart has cellular respiration and is nourished by the blood stream. The contractile cells of the myocardial muscle facilitates its operations by controlling the electrochemical environment of the actual contractile cell. This happens within the contractile cell by the changes in the electrochemical status as is required for polarization (contraction) and repolarization (replenishment and rest) to make changes in the electro-chemical status by moving ions in and out of contractile chambers via xe2x80x9cwetxe2x80x9d channels that have xe2x80x9cgatesxe2x80x9d or xe2x80x9cdoors.xe2x80x9d This proper contraction of ions within the cell provides electrochemical energy to cause the contraction to happen. The signals from the SA and AV nodes add additional electricity to the electrochemical contractile cells to activate the contractile response. All of this electrical activity is measured in millivolts with the entire process never exceeding about one volt to cause the heart to pump blood.
When a heart contracts it is called depolarization and when it prepares itself to contract again it is called repolarization. Heretofore, it has been presumed that myocardium, or heart muscle, must be in a resting state lasting about 200 milliseconds before the depolarization can occur once again. This has been believed to be necessary because ions of the contractile cell need to replenish and rearrange themselves before the correct electrochemical balance is reached within the contractile cell. However, the heart is not limited to the conventional ideas of how contraction occurs and it does not necessarily need to rest before it can contract again.
In 1887 it was demonstrated that natural electrical impulses could be measured from the surface of the body in dog, man and cat. In 1903 the accurate electrocardiograph and the various deflections of the electrocardiogram used today identified respectively as p,q,r,s and t, were invented by William Einthoven. Thereafter followed a flurry of activity by mathematicians and scientists to study Einthoven""s tracings of heart electrical deflections measurements as a way of explaining how the heart actually worked. In so doing they developed the idea that a heart made a contraction, either pumping or depolarization, followed by a relaxation, resting or repolarization, period. Out of this came the accepted theory that stated that no electrical impulse applied to the heart during the resting phase could make it reactivate and contract again. Cardiologists accepted that the heart had no capability to be contracted and held in that state for any length of time; certainly not for many seconds or even minutes. Consequently, no state of the art commercial electrical shocking device can hold a given waveform for many seconds or minutes. Present devices"" defibrillation and pacing modes maximum output are unable to sustain a pulse for longer than about 80 milliseconds.
The natural contractile cell electrical activity ranges from approximately xe2x88x92100 millivolts (relaxation) to +20 millivolts (contraction) during a complete cycle. Among other things that can alter the exact voltage present in the contractile cell or cells are nutritional and medicinal. In addition emotional excitement, panic or sorrow can impact the performance of the contractile cells.
In approximately 250 milliseconds (ms) all of the events listed in Table 1 complete one cycle of the heart""s electrical activity. The time depicted is for an activation by a bio-electrical impulse traveling throughout the heart""s electrical conduction system for each event.
The naturally-generated bio-electrical impulses required to conduct the business of the heart has been understood to consist of rather brief and simple activations at millivolt levels of excitation as shown in Table 1. Following that understanding, defibrillator designs fire electrical shocks at thousands of volts for ten to forty milliseconds duration. Such electrical therapy is almost universally delivered via a direct current coming from a dischargeable capacitor.
The need to conduct various kinds of surgical procedures on the surface of the heart or its blood vessels is complicated by the movement intrinsic to a living heart. Therefore, some surgical repairs are conducted by lowering the temperature of the heart until it can be stopped while a cardiopulmonary bypass machine, or heart-lung machine, keeps the patient alive by keeping blood circulation with oxygenation in tact.
Other procedures such as coronary artery angioplasty can be conducted on the moving and living heart. Also endoscopic pericardioscope has been employed to make surgical procedures less invasive and less expensive than open chest surgery. Such surgery when done open-chested by means of a standard midline sternotomy followed by entry into the pericardial sac is quite invasive and traumatic compared with the pericardioscopic procedures employed through several small incisions.
Cardiac ruptures are increasingly recognized by twelve lead electrocardiograms and have evolved into good predictors of impending rupture. With this diagnosis, impending rupture is prevented from proceeding to an actual fatal rupture. Endoscopic techniques are evolving that use fibrin glue or several other glues that can be used to effect a repair of small defects. Tissue adhesive and laser welding of myocardial injuries may require paralysis of the heart for a matter of seconds to a minute or two to allow precise location and procedure to effect a correction.
Tissue adhesives may eventually replace sutures which have frequently pulled through areas being operated on, especially if an infarcted area has been buttressed or oversewn. Myocardial tissues are in general very delicate and working surgically on them while they are in motion are fraught with difficulty.
Having an ability to stop the motion of the heart and then to allow a normal sinus rhythm return after the repair procedure is completed is a useful tool when coupled with the endoscope. With the advancing technologies in diagnosing ever smaller defects which are repairable with ever lesser invasive procedures, the ability to bring the heart to a stand-still electrically in the operating suite offers a new dimension to the cardiac surgeon.
The complexities of the human electrical system are not fully understood, as yet. Certainly the theories that date back to the early twentieth century of how the cardiac contractile cell is activated may be flawed since there was no capability at that time in history to test or evaluate those ideas. In these early theories the depolarization or contracting of the individual cardiac cell by an electric current was thought to occur rapidly and then the cell was required to undergo a refractory (resting period) before ionic changes could occur to prepare the cell to contract again (repolarization). These theories say that during the refractory period no stimulus of electricity, whatever its magnitude, could make the contractile cell activate.
In other words, the present theory suggests that a heart can contract but then must rest before it can contract again. Further, the theory says that the ions that were driven out of the cell are recovered very much more slowly than they were driven out before a new contraction can be done. This is a sort of ionic replenishment and depletion.
It appears that certain electrical waveforms can direct the contractile capacity more firmly and that such waveforms do not require long refractory (rest) period before a new contraction can happen. It has been demonstrated in the animal heart, that a heart can be held in a contracted state for many seconds without giving it a rest (refractory) period. Furthermore, it appears that long-cycle contractile period extinguishes fibrillation and allow for rescue by making the myocardium susceptible to the reestablishment of a cyclic beat. But pulsing must start within a certain number of milliseconds after the release of the long contraction in order to recover heart function more surely and do this with low voltage.
The waveforms of the present invention can play a role in conditioning the ionic population of the contractile cell so that recovery from fibrillation can result in resuming pulse pacing after the extinguishment of fibrillation wave fronts.
There is a significant problem in clinical practice wherein hearts often return to fibrillation after defibrillation instead of recovering by beating (usually slowly). Current treatment practice is to await cardiac reaction by waiting and watching after a defibrillation shock. If a beat begins, usually slow in rate, medicinal injections are used to speed it up so that good oxygenation and blood circulation can be recovered by the victim.
A waveform is the specific mathematical shape of an electrical energy burst that is generated by an electronic device and sent, like a bolt of lightening, in the case of a defibrillator, into the human body. An electrical waveform is generated as a definable pulse of electricity which is either a transient burst of energy into a storage battery. The result is after enough electrical potential is replaced in the battery it is able to turn-over the starter which in turn allows the engine to run and in turn recharge the battery. An automobile utilizes another twelve volt source and several minutes or longer to jump-start a dead battery. This is not so with the heart, where thousands of volts in millionths of a second is the usual therapy for heart attack victims.
The shape of a waveform is its graphical representation. This shape can vary in many ways, such as positive or negative or longer or shorter. In addition, the ascending-slope of electricity can have infinite variations as can the descending-slope prior to extinguishment of the electrical burst of energy. Energy can be pulsed with spaces between the actual electrical stimulus -- and do this so fast that no detection of such xe2x80x9cenergy blanksxe2x80x9d can be seen except on an oscilloscope. Usually a capacitor is used to store the electrical energy before it has released it all at once to provide the shock to the chest.
Present-day waveforms utilized in defibrillators are truncated, exponential, damped sinusoidal and trapezoidal. Biphasic variants are available which reverses the polarity in the middle of the brief but high-voltage shock. The duration of a waveform generated from a present-day closed-chest defibrillator is usually about 20 but not likely longer than 40 milliseconds; for an external cardiac pacer it is typically 20 to 40 milliseconds.
Such waveforms utilized by state-of-the-art products have changed little from their earliest design. Existing external defibrillator technology has developed a marketplace and is producing product to service its customers, with little change in output waveform. However, implantable cardiac products are taking more advantage of software and chip technology to better control the outputs of their products but they still use 310 to 750 volts for defibrillation.
An objective of the present invention is to apply lesser voltage, but in a special waveform which exerts more delicate control of the contractile business of the heart. The present invention uses a different electronic waveform and significantly lower voltage for conducting defibrillation and pacing, as well as for cardiac paralysis to allow surgical treatment. This lower voltage is actually closer to the electrical energy generated biochemically by the human or animal heart than is currently being used for defibrillation. This technology uses voltages closer to the kind of voltage that can xe2x80x9ckeyxe2x80x9d into the ionic control of contraction. Consequently, much lower voltage and amperage can be used to treat heart attacks. This lower voltage approach is also useful in implantable devices designed for either defibrillation or pacing. The long-term availability of lower voltage and special waveforms is gentler on the cardiac structures.
The present invention provides an ability of up to three minutes of electrical paralysis at relatively low voltage. Such electrical activity can be ordered up in combinations of seconds and minutes. The device can contract the myocardium and hold it in a contracted predetermined period and then release it so that circulation and cardiac tone can be reestablished. At will the surgeon can also re-paralyze the heart to continue the medical procedure or repair.
The present invention embodies defibrillation ability as well as a means to deal with asystole, tachycardia or bradycardia. The ability to select the kind of waveform shape as well as voltage output via an amplitudinal selection section provides capabilities not available within the state of the art defibrillation and pacing equipment.
The present invention is of a monolithic device for providing defibrillation and pacing of a heart comprising: defibrillating circuitry and pacing circuitry which engages once defibrillation has been accomplished. The invention is also of a device for providing defibrillation of a human heart from outside the body comprising defibrillation circuitry having an electromotive force of less than or equal to approximately 200 volts. The invention is further of a device for providing pacing of a human heart from outside the body comprising pacing circuitry having an electromotive force of less than or equal to approximately 200 volts. The invention is additionally of a device for providing defibrillation of a heart comprising digital circuitry for generating a direct current waveform to the heart. The invention is yet further of a device for providing pacing of a heart comprising digital circuitry for generating a direct current waveform to the heart.
The invention is also of a method for providing defibrillation and pacing of a heart comprising: defibrillating the heart; and pacing the heart within approximately 20 msec of cessation of step a). The invention is further of a method for providing defibrillation of a human heart from outside the body comprising defibrillating with an electromotive force of less than or equal to approximately 200 volts. The invention is additionally of a method for providing pacing of a human heart from outside the body comprising pacing with an electromotive force of less than or equal to approximately 200 volts. The invention is still further of a method for providing defibrillation of a heart comprising digitally generating a direct current waveform to the heart. The invention is yet further of a method for providing pacing of a heart comprising digitally generating a direct current waveform to the heart.
The present invention is also a device for generating waveforms for myocardial control and the device comprises means for providing variable low voltage waveforms wherein each waveform has at least one pulse. The device further comprises means for varying the voltage magnitude of each of the pulses of the waveforms to selected voltages. The device further has means for varying the polarity of each of the pulses of the low voltage waveforms to selected polarities. Means for providing a refractory period between selected ones of the pulses of the waveforms are also included in the device. The device can further comprise means for varying the pulse width of each of the pulses of the waveforms to selected widths.
The present invention is further a method of controlling the myocardium and comprises the steps of generating variable low voltage waveforms that each comprise at least one pulse, and applying a selected waveform to the myocardium for a selected period of time. Generating variable low voltage waveforms, each having at least one pulse, comprises varying the voltage magnitude of the pulses to selected magnitudes. The step of generating variable low voltage waveforms further comprises varying the polarity of each of the pulses to selected polarities, and can also comprise providing a refractory period between selected ones of the pulses of the waveforms. Generating variable low voltage waveforms can also comprise varying the pulse width of each of the pulses to selected widths.
A primary object of the present invention is to provide means by which substantially lower voltages and currents can be used to control cardiac arrhythmias.
A primary object of the present invention is to provide an apparatus having selectable voltages and a family of waveform shapes to treat the heart.
Another primary object of the present invention is to utilize significantly weaker electrical forces to provide myocardial control and cardiac paralysis.
A primary advantage of the present invention is that the voltage effects on the patient are reduced.
A primary advantage of the present invention is that it is lightweight yet can operate for durations of three hours or more.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.